Create a chart on a dynamically created canvas in Angular-chart.js

Question

I have a div that will need to host a chart or table depending on an XHR response. In the chart case, I need the div contents to be replaced by a canvas element that chart.js uses to display a graph.

If I add the canvas element to the HTML code, angular-chart.js renders a graph. However, If I inject the canvas into a div using javascript, the canvas element will be in the dom but the chart will not be displayed.

How do I work around this?

HTML

<div ng-controller="ChartCtrl">
  <div>
    {{chart.name}}
    This works (doughnut):
    <canvas id="chart-{{$index}}" class="chart chart-doughnut" chart-data="chart.data" chart-labels="chart.labels"></canvas>
  </div>
  This Doesn't work ({{chart.type}}):
  <div id="chartDiv"> </div>
</div>

Javascript

var myApp = angular.module('myApp', ['chart.js']);

// Create the controller, the 'ToddlerCtrl' parameter 
// must match an ng-controller directive
myApp.controller('ChartCtrl', function ($scope) {
   var chart_div = $('#chartDiv');
   chart_div.empty();
   canvas_html = '<canvas id="chart-2" class="chart chart-doughnut" chart-data="chart.data" chart-labels="chart.labels"></canvas>';
   console.log(canvas_html)
   chart_div.append(canvas_html);
   //console.log(chart_div)
  $scope.chart =    {
     name: 'Chart 1',
     type: 'Doughnut',
     labels: ['EVSC', 'ISB'],
     data: [13, 44]
   };
});

Plunker Example: http://plnkr.co/edit/9JkANojIl8EXRj3hJNVH?p=preview

HiDeoo · Accepted Answer · 2016-07-25 10:33:47Z

1

+50

You're altering the structure of the DOM, you can't append your newly created element like that in a "vanilla" or "jQuery" way.

You need to compile your HTML string or DOM element into a template to produce a template function that will be linked to the scope. The process will walk the DOM tree and match DOM elements to directives.

// Instantiate the app, the 'myApp' parameter must match what is in ng-app
var myApp = angular.module('myApp', ['chart.js']);

// Create the controller, the 'ToddlerCtrl' parameter must match an ng-controller directive
myApp.controller('ChartCtrl', function ($scope, $compile) {
  canvas_html = '<canvas id="chart-2" class="chart chart-doughnut" chart-data="chart.data" chart-labels="chart.labels"></canvas>';

  var element = angular.element(canvas_html);
  $compile(element)($scope);
  angular.element('#chartDiv').append(element);

  $scope.chart =    {
     name: 'Chart 1',
     type: 'Doughnut',
     labels: ['EVSC', 'ISB'],
     data: [13, 44]
   };
});

You can check out the result in this Plunker example.

answered Jul 25, 2016 at 10:33

HiDeoo

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1 Comment

Lmwangi Over a year ago

Super! I'll need to digest this. Thanks for the quick answer!

Keegan G · Accepted Answer · 2016-07-29 02:43:39Z

@HiDeo's answer is spot on, but here is a simplified Directive to do the same thing (notice the $compile still). The chartData variable attached to the scope is the presets for Chartjs' charts, any will work - the only thing of note is the $watch that I have added to the update property: if you are going to be updating your charts I would suggest doing something like this just to keep your hands clean.

.directive('replaceWithChart',function($compile){
    return {
        restrict: 'A',
        scope: {
            chartData: '=replaceWithChart',
            height: '=',
            width: '='
        },
        compile: function(element){
            var canvasModel = angular.element('<canvas></canvas>');
            return {
                post: function postLink(scope,elem,attr){
                    elem.empty();
                    var canvas = canvasModel.clone();
                    elem.append($compile(canvas)(scope));

                    !scope.height && (scope.height = elem[0].style.height || (elem[0].offsetHeight || elem[0].clientHeight));
                    !scope.width && (scope.width = elem[0].style.width || (elem[0].offsetWidth || elem[0].clientWidth));

                    var chart = new Chart(canvas[0].getContext('2d'),scope.chartData);
                    canvas.attr('height',(canvas[0].style.height = scope.height + 'px'));
                    canvas.attr('width',(canvas[0].style.width = scope.width + 'px'));

                    scope.$watch('chartData.update',function(){
                        scope.chartData.update && !(scope.chartData.update = false) && chart.update();
                    });
                    elem.on('$destroy',chart.destroy.bind(chart));
                    // Fixed some rendering issue, but I can't remember which
                    window.setTimeout(function(){
                        var padding = elem[0].style.padding || (window.getComputedStyle(elem[0],null).getPropertyValue('padding'));
                        elem[0].style.padding = '0';
                        elem[0].style.padding = padding;
                        chart.resize();
                    },300); // Magic number - I found this worked best
                }
            };
        }
    };
})

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